Patients with psychogenic polydipsia (compulsive water drinking) comprise about 6% of the schizophrenic population. These patients are usually managed by imposed fluid restriction with symptomatic treatment for episodic water intoxication. Many of these patients have been shown to have inappropriate secretion of antidiuretic hormone (SIADH) which may be a factor in their episodes of hyponatremia. Demeclocycline is an antibiotic related to tetracycline which blocks the action of antidiuretic hormone (ADH) and is useful in treating SIADH of diverse etiologies. Preliminary study has suggested that demeclocycline might be useful in psychiatric patients with psychogenic polydipsia.